1. Field of the Invention
The present invention relates to a backlight assembly for emitting flat light, and a liquid crystal display having the same.
2. Discussion of the Related Art
Flat display devices are generally divided into emissive type flat display devices and non-emissive type flat display devices. The emissive type flat display devices include plasma display devices and electro-luminescent display devices. In contrast, the non-emissive type flat display devices include liquid crystal displays (LCDs), as a representative example thereof.
The LCDs control an amount of transmission of light that is incident from the outside, because they do not spontaneously emit the light. For this reason, the LCDs have difficulty in displaying an image in a dark place. To solve this problem, each LCD is equipped with a backlight assembly, which emits flat (or two-dimensional) light. The backlight assembly irradiates the light to the rear surface of a liquid crystal panel of the LCD. Further, the backlight assembly is used in flat panel graphic displays, such as lighting signs, in addition to the non-emissive type display devices, such as LCDs.
This backlight assembly is divided into a direct type and an edge type according to the arrangement of a light source. The direct-type backlight assembly has a plurality of light sources disposed below a radiating surface of the light. The light sources directly emit light to the rear surface of a light irradiating target (i.e. a liquid crystal panel). Meanwhile, the edge-type backlight assembly includes a light source installed on one side of a light guide plate, and the light guide plate guides the light from the light source to the entire surface of the liquid crystal panel. The light guide plate causes the light generated from the light source to radiate to the rear surface of the target (i.e. the liquid crystal panel) in the form of flat light.
In comparison with the direct-type backlight assembly, the edge-type backlight assembly remarkably reduces power consumption. As the size of the LCD having the edge-type backlight assembly is gradually increased, the brightness of an image displayed by the LCD is decreased. In this aspect, the edge-type backlight assembly is applied to a relatively small size of LCD such as the monitor of a lap-top computer or a small-sized desk top computer.
FIG. 1 is an exploded perspective view illustrating a related LCD having an edge-type backlight assembly, and FIG. 2 is a sectional view taken along line I-I′ of the related LCD of FIG. 1. Referring to FIGS. 1 and 2, the related LCD includes a liquid crystal panel 10 displaying an image, a backlight assembly 20 providing flat light to the rear surface of the liquid crystal panel 10, and a top case 11 enclosing an edge of the liquid crystal panel 10 and sides of the backlight assembly 20.
The backlight assembly 20 includes a bottom cover 80 fastened with a support main 40. A lamp 60, a lamp housing 61, a reflector 70, a light guide plate 50, and a set of optical sheets 30 are received into the support main 40, and are supported by the bottom cover 80. The support main 40 supports the liquid crystal panel 10.
The light guide plate 50 allows light emitted from the lamp 60 to travel to the liquid crystal panel 10 in the form of flat light. To this end, the light guide plate 50 is made of material having superior light transmittance. In addition, the light guide plate 50 has a prism pattern capable of increasing an amount of the flat light. Although not illustrated, the prism pattern is formed on the rear surface of the light guide plate 50.
The lamp 60 is disposed near one side of the light guide plate 50 so as to be in one plane by the light guide plate 50. The light emitted from the lamp 60 is incident onto one side (hereinafter, referred to as “incident plane”) of the light guide plate 50. The lamp 60 is provided with electrodes 63 at opposite ends thereof. An entire length of the lamp 60 does not exceed the incident plane of the light guide plate 50. This functions to prevent the size of the LCD from exceeding an effective screen of the liquid crystal panel 10.
The lamp housing 61 reflects some of the light, which is emitted from the lamp 60 toward to the other directions than the incident plane of the light guide plate 50, to the incident plane of the light guide plate 50, thereby increasing the efficiency of using the light emitted from the backlight assembly.
In the related LCD having the edge-type backlight assembly, the electrodes 63 of the lamp 60 correspond to opposite ends of the incident plane of the light guide plate 50. An amount of the light that is incident onto the opposite ends of the incident plane of the light guide plate 50 is relatively smaller, compared to the other portion of the incident plane of the light guide plate 50. As such, an amount of the light that exits from corner regions (black regions of FIG. 1) of the light guide plate 50 on the side of the incident plane of the light guide plate 50 is relatively smaller, compared to the other surface regions of the light guide plate 50. In other words, the related edge-type backlight assembly has no alternative but to emit a remarkably small amount of light from some of the surface regions corresponding to the electrodes 63 of the lamp 60. As a result, the image displayed on the liquid crystal panel 10 inevitably has shadows (dark portions). The non-uniform brightness caused by the shadows degrades a quality of the image displayed by the LCD.
In order to inhibit the shadows from being generated, the edge-type backlight assembly is provided with a plurality of diffusion sheets. However, these diffusion sheets have difficulty in making the LCD lightweight, thin, and inexpensive, and furthermore cannot sufficiently inhibit the shadows and the non-uniform brightness caused by the shadows.
In addition, the light incident onto the incident plane of the light guide plate 50 includes the light (hereinafter, referred to as “direct light”) that is directly incident from the lamp 60, and the light (hereinafter, referred to as “reflected light”) that is reflected by the lamp housing 61. The reflected light is incident onto the incident plane of the light guide plate 50 at a large angle with respect to the surface of the light guide plate 50, compared to the direct light. As such, the light guide plate 50 allows a lot of light to be irradiated in the proximity of the incident plane of the light guide plate 50. More specifically, as illustrated in FIG. 2, the light guide plate 50 has a spectral region (i.e. bright lines (bright band)) Ws where a lot of light is irradiated, and a spectral region (i.e. dark lines (dark band)) Bs where a relatively small of light is irradiated. In other words, the related edge-type backlight assembly has difficulty in irradiating uniform flat light to the liquid crystal panel. The non-uniformity of this flat light leads to the bright lines (bright band) and the dark lines (dark band) within the image displayed on the liquid crystal panel 10. As a result, the LCD using the edge-type backlight assembly not only has difficulty in displaying the image having uniform brightness but also has no choice but to deteriorate the image quality.